Natural Inclusions in Tanzanite: Crystals, Cleavage, Fissures & Clarity

Tanzanite is one of the youngest major gemstones in the modern jewelry world, yet it has developed an extraordinary identity.

Its color can move between blue, violet and purple as the viewing direction changes.

Its finest stones can display deep saturation and flashes of different pleochroic colors as they move through light.

And unlike gemstones mined across several continents, tanzanite is associated with a remarkably limited geographic source.

That rarity contributes to its appeal.

But the internal world of tanzanite is equally interesting.

Natural stones can contain mineral crystals, fluid inclusions, fracture features, growth interruptions, cleavage related structures and, in rare examples, unusual metallic whisker like inclusions.

For the broader foundation on natural inclusions, begin with the Natural Gemstone Inclusions Guide .

What Is Tanzanite?

Tanzanite is the blue to violet gem variety of the mineral zoisite.

Its extraordinary appearance is associated with strong pleochroism, meaning the crystal can display different colors when viewed along different directions.

A single crystal can show blue, violet and other color components depending on orientation.

That property makes cutting unusually important.

The cutter must decide how to orient the rough to balance face up color, weight retention and brilliance.

The result is that two tanzanites of similar size can present very differently depending on orientation and cutting.

Where Does Tanzanite Come From?

Tanzanite is associated with the Merelani mining area of northern Tanzania.

This highly localized source is one of the gemstone's defining characteristics.

The geological environment that produced tanzanite also produced an unusually rich mineral assemblage.

That environment helps explain why some rare tanzanite specimens can contain unusual mineral inclusions.

Most faceted jewelry tanzanite, however, is comparatively clean.

Are Inclusions Normal in Natural Tanzanite?

Yes.

Natural tanzanite can contain inclusions.

But fine faceted tanzanite is generally expected to have high transparency and few or no inclusions visible to the unaided eye.

This distinction is important.

A tiny crystal visible only under magnification may have almost no practical effect.

A large dark inclusion directly beneath the table can be considerably more important.

A significant fracture can affect both appearance and durability.

The buyer should therefore evaluate what the inclusion actually does rather than simply whether one exists.

Crystal Inclusions in Tanzanite

Natural tanzanite can contain crystals of other minerals that became enclosed during growth.

These inclusions may appear transparent, pale, dark or metallic depending on their composition.

A small crystal near the girdle may disappear during ordinary viewing.

A high contrast crystal directly beneath the table can attract more attention.

For collectors, unusual crystal inclusions can provide a fascinating microscopic connection between tanzanite and the mineral rich environment in which it formed.

Graphite and Dark Mineral Inclusions

Dark mineral inclusions can occur in natural tanzanite.

Graphite is one of the opaque minerals associated with the Merelani geological environment and has been observed in and around tanzanite bearing material.

Because transparent blue violet zoisite provides a relatively bright host, opaque dark inclusions can create strong contrast.

Their effect on value depends heavily on position and visibility.

A tiny dark inclusion may be invisible face up.

A centrally located feature can become much more noticeable.

Rare Merelaniite Whiskers

One of the most unusual inclusion scenes documented in tanzanite involves the rare mineral merelaniite.

Under magnification, merelaniite can appear as slender dark metallic whiskers.

Some are gently curved.

Some branch.

In rare included specimens they can extend through the blue violet tanzanite like microscopic metallic threads.

This is not a common inclusion that buyers should expect to find in ordinary faceted tanzanite.

Its rarity is precisely what makes the feature interesting to collectors.

Growth Blockages

Crystal growth is not always uninterrupted.

If another mineral or foreign body interferes with the developing zoisite crystal, growth can be temporarily blocked.

The resulting internal structure can preserve evidence of that interruption.

Rare documented tanzanite specimens have shown growth blockages associated with unusual mineral inclusions.

Some of these areas can contain fluid or dark solid material.

For a collector, this provides an extraordinary glimpse into the physical process of crystal formation.

Fluid Inclusions in Tanzanite

Fluid containing cavities can occur in natural tanzanite.

Some may appear independently.

Others can be associated with growth blockages or fracture systems.

The visual effect depends upon concentration and size.

Small microscopic fluid inclusions may have no effect on face up beauty.

Dense or reflective fluid related structures can become more apparent under magnification.

They can also preserve useful evidence about the gemstone's geological and treatment history.

Can Fluid Inclusions Reveal Heat History?

In certain unusual tanzanite specimens, intact fluid inclusions can provide evidence relevant to heat treatment interpretation.

Heat can alter or destroy some internal fluid features depending on the conditions involved.

That means preserved liquid inclusions can sometimes provide useful evidence that a particular specimen did not experience treatment conditions sufficient to disrupt them.

This should not be simplified into a universal rule.

Treatment interpretation requires the full microscopic and gemological scene.

Natural Fissures in Tanzanite

Natural tanzanite can contain fractures and fissures.

Some are completely internal.

Others can intersect the polished exterior.

A fine internal fissure visible only through magnification may have limited practical effect.

A broad reflective fracture can interrupt transparency and brilliance.

A large open fracture can also influence durability.

Because fine jewelry tanzanite is generally expected to be comparatively clean, significant fractures deserve careful consideration.

Surface Reaching Inclusions in Tanzanite

A natural fracture can extend to the polished surface.

That makes it surface reaching.

The phrase describes the location of the feature.

It does not automatically establish recent damage.

It also does not automatically establish that a filler or clarity enhancement is present.

For the complete explanation, read Surface Reaching Inclusions in Natural Gemstones .

Tanzanite and Cleavage

Cleavage is different from an ordinary random fracture.

It describes a mineral's tendency to separate along particular structural directions.

Zoisite has cleavage directions that deserve consideration during cutting, setting and wear.

A cleavage related feature may appear as a planar separation inside the gemstone.

That does not mean every visible plane in tanzanite is cleavage.

Proper identification depends upon its orientation and microscopic character.

Iridescent Cleavage Features

Some natural tanzanite specimens can display vivid iridescent colors along fine separations associated with cleavage planes.

Under suitable lighting, these microscopic separations can produce rainbow like interference colors.

The effect can be striking.

In ordinary jewelry evaluation, a major cleavage related separation may deserve durability consideration.

In a collector specimen under magnification, subtle iridescence can create a remarkable internal visual feature.

Why Eye Visible Inclusions Matter More in Tanzanite

Fine faceted tanzanite commonly reaches the market with high apparent clarity.

That availability creates a meaningful expectation for transparency.

An inclusion can therefore affect value more strongly than a similar feature might in emerald.

A buyer evaluating two similarly colored and similarly cut tanzanites may reasonably prefer the cleaner stone if both are offered at similar prices.

The exception is when an unusual inclusion creates specific collector interest.

How Inclusion Type Changes the Buying Decision

Most Blue Tanzanite Is Heat Treated

Heat treatment is an established part of the modern tanzanite market.

Much naturally occurring zoisite from the deposit shows brownish, violet or mixed colors before heating.

Controlled heating can reveal or strengthen the blue and violet colors for which tanzanite is famous.

The trade generally assumes that most blue tanzanite has been heated.

Because heating is so widespread and accepted, it usually has much less impact on value than treatment does in gemstones where untreated material commands a large premium.

Can a Laboratory Always Determine Whether Tanzanite Was Heated?

Not necessarily.

Heat treatment in tanzanite can be difficult to identify definitively.

This is one reason the market commonly assumes that blue material has been heated unless strong evidence indicates otherwise.

Certain unusual inclusion scenes can contribute useful evidence.

But treatment status should not be declared from one visible crystal or fissure alone.

The complete gemological picture matters.

Rare Cat's Eye Tanzanite

Although most tanzanite is faceted to emphasize color and brilliance, rare material can contain oriented inclusions capable of producing chatoyancy.

When suitable rough is cut as a cabochon, reflected light can form a bright band across the gemstone.

This creates a cat's eye effect.

In this situation, the inclusions responsible for the phenomenon become an essential positive feature rather than an ordinary clarity concern.

Color Versus Clarity in Tanzanite

Color is one of the most important value factors in tanzanite.

Deeply saturated violet blue and blue violet stones can command much stronger prices than pale material.

But strong color does not erase clarity concerns entirely.

A significant fracture can still reduce value substantially.

A large dark inclusion can remain distracting.

The most desirable faceted tanzanites generally combine rich color, good transparency, lively cutting and minimal distracting inclusions.

For a deeper look at color evaluation, explore the Gemstone Color Guide: Understanding Hue, Tone and Saturation .

Why Pleochroism Changes the Visual Experience

Tanzanite can show different colors when viewed from different crystal directions.

That means an inclusion can also become more or less noticeable as the stone moves.

A dark feature may be concealed against one direction of stronger body color and become more obvious against another.

The cutter must therefore consider both color orientation and clarity when positioning the stone.

Video can be especially useful when evaluating tanzanite because a still photograph captures only one orientation.

How Cutting Interacts With Inclusions

Tanzanite cutters must balance several competing goals.

They want attractive face up color.

They want good brilliance.

They want to retain valuable carat weight.

And they may need to work around fractures or inclusions present in the rough.

A cutter may place a small inclusion near the girdle rather than beneath the table.

A vulnerable fracture may require material to be removed.

Cutting orientation can also determine whether blue or violet dominates the finished gemstone.

This is why cut quality and inclusion placement should be evaluated together.

Tanzanite Versus Sapphire

Tanzanite and sapphire can both display rich blue color, but they are very different minerals.

Their durability, inclusion patterns and optical behavior differ.

Natural sapphire can contain silk, crystals, healed fissures and growth features.

Fine faceted tanzanite is generally expected to be comparatively clean.

The two should therefore not be judged by exactly the same clarity or wear expectations.

For the companion guide, read Natural Inclusions in Sapphire .

Why Fractures Matter to Tanzanite Durability

Tanzanite can be worn successfully in jewelry, but it deserves thoughtful care.

It is not as hard or forgiving as ruby or sapphire.

A clean gemstone can already require protection from hard blows.

A significant fracture increases the importance of that consideration.

Features approaching an edge, corner or setting pressure location deserve special attention.

A jeweler should know about important fractures before applying pressure during setting.

Choosing Jewelry for an Included Tanzanite

Why Macro Photography Can Make Tanzanite Look More Included

A microscopic crystal can become a dominant feature when a small gemstone fills an entire screen.

A fine fissure can look like a major crack.

A tiny cleavage separation can become visually dramatic.

The photograph may be completely accurate.

The scale is simply very different from ordinary viewing.

Compare macro photographs with normal face up photographs and video.

Ask whether the inclusion is visible to the unaided eye.

For tanzanite, that question matters because fine faceted material is normally expected to have good visible clarity.

Eye Clean Does Not Mean Inclusion Free

A beautiful transparent tanzanite can appear perfectly clean during normal viewing while containing microscopic crystals, fluid features or growth structures.

Eye clean describes the visible presentation.

It does not mean the crystal contains no natural internal characteristics.

This distinction becomes particularly important in online buying where extreme macro photography may reveal details that would never be visible during normal wear.

What Buyers Should Look for in Natural Tanzanite

When Should You Pass on an Included Tanzanite?

A tanzanite may deserve a pass when its inclusions substantially reduce the qualities for which fine faceted tanzanite is valued.

A large dark crystal directly beneath the table can dominate the appearance.

Dense inclusion can reduce transparency.

A broad open fracture can create unnecessary durability concerns.

A heavily fractured stone priced like cleaner material may simply offer poor value.

Because eye clean faceted tanzanite is widely available, there is generally little reason to accept severe clarity problems without receiving something meaningful in return.

When an Included Tanzanite Can Be an Exceptional Choice

A microscopic inclusion with no face up effect may be almost irrelevant to the wearing experience.

A strongly saturated tanzanite can remain beautiful with a modest natural feature near the edge.

A rare mineral inclusion may create genuine collector interest.

An iridescent cleavage feature may be fascinating under controlled magnification.

A rare chatoyant specimen may rely on inclusions to create its optical phenomenon.

The useful question remains:

What does this particular inclusion actually do to this particular tanzanite?

Collector Appeal: A Rare Gemstone With an Even Rarer Microscopic World

Tanzanite's geographic rarity already makes it unusual.

Its microscopic world can make an individual specimen even more distinctive.

A fluid filled growth blockage can record interrupted crystal development.

A dark crystal can preserve another mineral within the zoisite.

A metallic whisker can introduce an exceptionally rare mineral inclusion.

An iridescent cleavage plane can create colors within a gemstone already famous for extraordinary color.

These features remind collectors that gemstone rarity exists at more than one scale.

Frequently Asked Questions

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